[Bob Kontak]

Under the passenger seat there is an oxygen sensor relay that can fail. It is a square/cube relay on the Lambda box that can be unplugged easily. Unplug it and see if symptoms change. I bet that is the issue.

Two years ago, a member here in Houston had the same symptoms when it was hot outside. Turned out to be the wiring connection was corroded on the engine firewall on the drivers side that connected the frequency valve to the O2 relay. That connection is reachable by hand and just unplugging and replugging it may help the connection.